Why Japanese Homes Are Freezing in Winter

Visitors arriving in Japan in January are frequently prepared for the cold outside and completely unprepared for the cold indoors. Hallways, bathrooms and toilets are often barely warmer than the street. This is not poverty or eccentricity — it is the result of a specific set of historical and regulatory choices.

Houses built for summer, not winter

The philosophy is old enough to be quotable. In the fourteenth-century essay collection Tsurezuregusa, Yoshida Kenkō wrote that a house should be built with summer in mind, because you can endure the cold but suffer badly in the heat.

That instinct made sense. Japanese summers are hot and extremely humid, and before air conditioning the only defence was airflow. Traditional construction — sliding paper screens, raised floors, deep eaves, minimal solid walls — is essentially a machine for moving air through a building. It works beautifully in August and is close to useless in February.

The regulatory gap

The more surprising part is how long this persisted into the modern era. Japan's residential energy efficiency and insulation guidelines went largely untouched for over two decades, and for most of that period they were guidelines rather than binding requirements — unlike the mandatory insulation codes long standard across Europe and North America. Standards have been tightened in recent years, but the existing housing stock reflects decades of building without them.

The measurable result: nationwide surveys have found the average living-room temperature in Japanese homes during winter, while occupants are at home, sits around 17°C — below the 18°C minimum the World Health Organization recommends for healthy adults. In unheated rooms the figure is considerably lower.

There is a genuine health cost attached. The sharp temperature difference between a heated living room and a freezing bathroom is linked to heat shock — a blood pressure spike on undressing and entering hot water that contributes to a significant number of bathroom deaths in Japan each winter, disproportionately among the elderly.

How people actually stay warm

The Japanese solution is not to heat the house. It is to heat the person, or at most the room they are in.

The kotatsu is the centrepiece. A low table with an electric heater fixed to its underside and a thick quilt sandwiched between the frame and the tabletop. You sit on the floor with your legs underneath. It heats a volume of roughly one duvet rather than a house, which makes it extraordinarily cheap to run and extraordinarily hard to get out of. Winter evenings in a great many Japanese households are spent entirely within a two-metre radius of one.

Kerosene fan heaters are still widely used, particularly in colder regions. They require regular airing of the room.

Other standard equipment: reverse-cycle air conditioners doing double duty as heaters, kerosene fan heaters, electric carpets, heated toilet seats, hanten padded jackets worn indoors, and disposable stick-on heat pads (kairo) sold by the box in every convenience store.

What this means for visitors

• A traditional ryokan may be colder than you expect at night, though the futon bedding is warmer than it looks.
• The bathroom will be cold. This is precisely why the deep, very hot bath exists, and why onsen and sento culture is not merely recreational.
• Pack indoor layers, not just outdoor ones. Thermal socks matter more than a heavier coat.
• Buy kairo heat pads at any convenience store on day one. They cost a few hundred yen for a pack and stay warm for hours.

Newer apartments and hotels are considerably better insulated, and the standards are improving. But the underlying attitude — that you dress for the indoors, rather than heating the indoors to suit how you dress — remains one of the most quietly foreign things about winter in Japan.